During the current phase of this grant, the feasibility of using single focused ultrasound transducer guided by MRI has been demonstrated in clinical treatments of fibroadenomas of the breast. In addition, several basic safety and monitoring issues related to the therapy were investigated in animal experiments and it was shown that MRI monitoring can be used not only to guide and monitor the location of the focal spot but also shown that MRI monitoring can be used not only to guide and monitor the location of the focal spot but also to detect the actual temperature elevation achieved. This result exceeded our expectations and will allow us to use MRI to provide online dosimetry. The overall objective of this proposal is to test the hypothesis that MRI guided and monitored focused ultrasound surgery can be effectively used in combination with radiation therapy to coagulate small malignant tumors of the breast. As was shown by our treatments of fibroadenoma of breast the small focal spot size of the clinical device makes the treatment of typical target volumes required for breast cancer impractical. To overcome this, we have developed phased array systems (under another grant) that can increase the focal volume and reduce the treatment time. The utilization of the phased arrays allow us to make the thermal exposure distribution uniform and use the minimum amount of power to reduce the total treatment time. However, previous experience with tissue coagulation has been primarily with single focused transducers that deliver very non-uniform and high thermal dose in the target volume. Thus, we plan to execute a series of rabbit VX2 carcinoma sonications to establish the dose. In addition the clinical treatments of the fibroadenomas will be continued to test the treatment procedures in clinical settings. Finally, we plan to execute a clinical phase I trial to test the feasibility of treating malignant breast tumors by using MRI guided focused ultrasound.